排序方式： 共有76条查询结果，搜索用时 109 毫秒
71.
Erwan Gloaguen Denis Marcotte Michel Chouteau Herv Perroud 《Journal of Applied Geophysics》2005,57(4):242-259
A new radar velocity tomography method is presented based on slowness covariance modeling and cokriging of the slowness field using only measured travel time data. The proposed approach is compared to the classical LSQR algorithm using various synthetic models and a real data set. In each case, the proposed method provides comparable to or better results than LSQR. One advantage of this approach is that it is self-regularized and requires less a priori information. The covariance model also allows stochastic imaging of slowness fields by geostatistical simulations. Stable characteristics and uncertain features of the inverted models can then be easily identified. 相似文献
72.
Luca Sitzia Pascal Bertran Stphane Boulogne Michel Brenet Rmy Crassard Anne Delagnes Marine Frouin Christine Hatt Jacques Jaubert Lamya Khalidi Erwan Messager Norbert Mercier Alain Meunier Stphane Peign Alain Queffelec Chantal Tribolo Roberto Macchiarelli 《Geoarchaeology》2012,27(6):471-491
The Shi'bat Dihya 1 site in western Yemen, dated by optically stimulated luminescence to 55 ka, provides insight into the Middle Paleolithic peopling of the Arabian Peninsula. The archaeological layer is interstratified within thick, sandy silt floodplain deposits filling a piedmont basin. Luminescence dates, lack of soil development, and gypsum precipitation indicate a high accretion rate of the floodplain during Marine Isotope Stage 3, in connection with a (semi)‐arid environment. Rapid overbank sedimentation was likely a result of the remobilization of loess material deposited on the Yemeni Great Escarpment at the periphery of the adjacent Tihama coastal sand desert or of other sources. Fabric and size analyses of the lithic artifacts, together with spatial projections, indicate site modifications by floods. Primary modifications include (1) selective accumulation of medium‐sized lithic pieces as a result of hydraulic sorting, (2) bimodal orientation of artifacts, and (3) ripple‐like arrangement of lithics and bone/tooth fragments. The overrepresentation of teeth may also be a consequence of sorting. Although floods have distorted the original site patterning, long‐distance transport of artifacts by water can be excluded, as indicated by relatively high refitting rate, close proximity of artifacts derived from the same block of raw material, and lack of abrasion of the pieces. Therefore, the site is considered “geologically” in situ because its remobilization by water occurred shortly after human abandonment. This study also stresses that the effective preservation of a site cannot be assessed without careful taphonomic study, even in a potentially favorable depositional context such as silty alluvium. 相似文献
73.
The prediction of fluid flows within hydrocarbon reservoirs requires the characterization of petrophysical properties. Such characterization is performed on the basis of geostatistics and history-matching; in short, a reservoir model is first randomly drawn, and then sequentially adjusted until it reproduces the available dynamic data. Two main concerns typical of the problem under consideration are the heterogeneity of rocks occurring at all scales and the use of data of distinct resolution levels. Therefore, referring to sequential Gaussian simulation, this paper proposes a new stochastic simulation method able to handle several scales for both continuous or discrete random fields. This method adds flexibility to history-matching as it boils down to the multiscale parameterization of reservoir models. In other words, reservoir models can be updated at either coarse or fine scales, or both. Parameterization adapts to the available data; the coarser the scale targeted, the smaller the number of unknown parameters, and the more efficient the history-matching process. This paper focuses on the use of variational optimization techniques driven by the gradual deformation method to vary reservoir models. Other data assimilation methods and perturbation processes could have been envisioned as well. Last, a numerical application case is presented in order to highlight the advantages of the proposed method for conditioning permeability models to dynamic data. For simplicity, we focus on two-scale processes. The coarse scale describes the variations in the trend while the fine scale characterizes local variations around the trend. The relationships between data resolution and parameterization are investigated. 相似文献
74.
High-order Statistics of Spatial Random Fields: Exploring Spatial Cumulants for Modeling Complex Non-Gaussian and Non-linear Phenomena 总被引：9，自引：7，他引：2
The spatial distributions of earth science and engineering phenomena under study are currently predicted from finite measurements
and second-order geostatistical models. The latter models can be limiting, as geological systems are highly complex, non-Gaussian,
and exhibit non-linear patterns of spatial connectivity. Non-linear and non-Gaussian high-order geostatistics based on spatial
connectivity measures, namely spatial cumulants, are proposed as a new alternative modeling framework for spatial data. This
framework has two parts. The first part is the definition, properties, and inference of spatial cumulants—including understanding
the interrelation of cumulant characteristics with the in-situ behavior of geological entities or processes, as examined in
this paper. The second part is the research on a random field model for simulation based on its high-order spatial cumulants.
Mathematical definitions of non-Gaussian spatial random functions and their high-order spatial statistics are presented herein,
stressing the notion of spatial cumulants. The calculation of spatial cumulants with spatial templates follows, including
anisotropic experimental cumulants. Several examples of two- and three-dimensional images, including a diamond bearing kimberlite
pipe from the Ekati Mine in Canada, are analyzed to assess the relations between cumulants and the spatial behavior of geological
processes. Spatial cumulants of orders three to five are shown to capture directional multiple-point periodicity, connectivity
including connectivity of extreme values, and spatial architecture. In addition, they provide substantial information on geometric
characteristics and anisotropy of geological patterns. It is further shown that effects of complex spatial patterns are seen
even if only subsets of all cumulant templates are computed. Compared to second-order statistics, cumulant maps are found
to include a wealth of additional information from underlying geological patterns. Further work seeks to integrate this information
in the predictive capabilities of a random field model. 相似文献
75.
La présente étude a pour objectif d’analyser la variabilité spatiale multi-échelles de l’équivalent en eau de la neige (EEN). Dans un premier temps, la variabilité spatiale de l’EEN par rapport à la latitude et à la longitude a été analysée. Des indices locaux ont été utilisés pour caractériser les différentes structures spatiales. Par la suite, les structures spatiales homogènes ont été délimitées à l’aide de l’approche de segmentation spatiale multi-résolutions en utilisant des méta-variables physiographiques. La segmentation a été validée à l’aide du test non paramétrique de Kruskal-Wallis appliqué aux données de l’EEN de chaque paire de zones adjacentes. À l’échelle régionale, la segmentation spatiale a permis d’identifier six zones géographiques différenciées par leur position par rapport aux modes de circulations atmosphériques et la disposition du relief. À l’échelle locale, la segmentation spatiale montre le rôle de la pente, de la courbure, etc. dans la variabilité spatiale du couvert nival.
Editeur Z. W. Kundzewicz; Editeur associé E. Gargouri 相似文献
76.
The round-trip travel time measurements made by spacecraft laser altimeters are primarily used to construct topographic maps
of the target body. The accuracy of the calculated bounce point locations of the laser pulses depends on the quality of the
spacecraft trajectory reconstruction. The trajectory constraints from Doppler and range radio tracking data can be supplemented
by altimetric “crossovers”, to greatly improve the reconstruction of the spacecraft trajectory. Crossovers have been used
successfully in the past (e.g., Mars Orbiter Laser Altimeter on Mars Global Surveyor), but only with single-beam altimeters.
The same algorithms can be used with a multi-beam laser altimeter, but we present a method using the unique cross-track topographic
information present in the multi-beam data. Those crossovers are especially adapted to shallow (small angle) intersections,
as the overlapping area is large, reducing the inherent ambiguities of single-beam data in that situation. We call those “swath
crossovers”. They prove particularly useful in the case of polar-orbiting spacecraft over slowly rotating bodies, because
all the non-polar crossovers have small intersection angles. To demonstrate this method, we perform a simplified simulation
based on the Lunar Reconnaissance Orbiter (LRO) and its five-beam Lunar Orbiter Laser Altimeter. We show that swath crossovers
over one lunar month can independently, from geometry alone, recover the imposed orbital perturbations with great accuracy
(5 m horizontal, < 1 m vertical, about one order of magnitude smaller than the imposed perturbations). We also present new
types of constraints that can be derived from the swath crossovers, and designed to be used in a precision orbit determination
setup. In future work, we will use such multi-beam altimetric constraints with data from LRO. 相似文献